Field of Inventions
The field of this application and any resulting patent relates to formation pressures, particularly for oil and gas wells.
Description of Related Art
Drilling an oil or gas well requires controlling density of the drilling mud so wellbore pressure remains higher than the pore fluid pressure in any formation along the uncased borehole. Otherwise, formation fluid may flow into the wellbore and cause a kick, which can lead to blowouts if inflow is not stopped before the formation fluid reaches the top of the well. Excessive overbalance of the wellbore pressure may also cause problems, such as sticking of the drill pipe, inducing fractures in the borehole wall resulting in drilling fluid loss, and reducing penetration rate of the drill bit. Therefore, operators adjust the mud weight according to the varying pore pressures along the wellbore.
Seismically-derived interval velocities may develop pre-drill pore pressure predictions for oil and gas wells. However, reliability and/or complexity of these predictions impacts drilling performance. Prior velocity transforms to effective stress approaches for the predictions fail to recognize that a single velocity-effective stress relation is not always sufficient. Estimations must take account of compaction, unloading, and differences in formation lattice structures, such as smectite, which is a swelling clay, and illite, which is a non-swelling clay. For example, clay type, clay volume, sediment provenance, formation age, sedimentation rate, and diagenesis may each play a role in altering velocity-effective stress relationships. Existing methods that require calculation of coefficients make predictions difficult and slow, which also limits real-time use when drilling.
Therefore, a need exists for improved systems and methods to provide determinations of pore pressure in formations.
Various methods and systems have been proposed and utilized for determining pore pressure of a formation, including the methods and systems disclosed in the references appearing on the face of this patent. However, these methods and systems lack all the steps and/or features of the methods, systems, and computer-readable media covered by the patent claims below. Furthermore, it is contemplated that the methods, systems, and computer-readable media covered by at least some of the claims of this issued patent solve many of the problems that prior art methods and systems have failed to solve. Also, the methods, systems, and computer-readable media covered by at least some of the claims of this patent have benefits that could be surprising and unexpected to a person of ordinary skill in the art based on the prior art existing as of the filing date of this application.